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Looking at it again I am not sure it is good practice to use the same colour wires as far as I am concern.
I am having difficulty seeing the connection under the board, maybe a photo of the underside would be good but is look like D3 track goes under the rail 0V to R4/R3 V divider arrangement but it is really hard to see. There is a bit of black gunge blocking near D3 view of that area.
I can't imagine a 555 running without some sort of regulator as it may produce varying pulses. I also can't imagine putting a diode across the rail without a inline fuse to protect against reverse polarity.
Without a photo of the underside of the board I feel it is difficult to assume.
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